1. Field
The present invention relates to methods of manufacturing EL display devices.
2. Description of the Related Art
In recent years, next-generation display devices have been actively developed. Among others, an EL (Electroluminescence) display device receives much attention which has a driving substrate on which first electrodes, a plurality of organic layers including light emitting layers, and second electrodes are laminated in this order. The EL display device features a wide viewing angle because of being self-luminous, power saving expectable due to no need for a backlight, high responsiveness, a thin depth of the device, and the like. For this reason, introduction of the EL display device has been strongly desired into applications for large screen display devices such as television receivers.
In applications of color display, a display technology using three-color pixels, i.e. red, blue, and green colors, is most commonly employed. Besides it, aiming at improving power saving, reliability, etc., developments of other display technologies have been advanced at various manufactures, by using four-color pixels, i.e. red, blue, green, and white colors, or alternatively red, blue, green, and light-blue colors or the like.
In an organic EL light-emitting element, it is required to form, for every pixel, an organic EL light-emitting part for each of three colors of red, blue, and green, or alternatively for each of four colors of such as red, blue, green, and white.
The most common process for forming discrete organic EL parts is such that a fine-metal mask having fine holes is used to form the organic EL parts only at locations corresponding to the holes, by vapor deposition through the mask. For example, a red-color fine-metal mask is used to form the organic EL parts to emit red light by vapor deposition through it a green-color fine-metal mask is used to form the organic EL parts to emit green light by vapor deposition through it; a blue-color fine-metal mask is used to form the organic EL parts to emit blue light by vapor deposition through it. This completes the light emitting parts to emit respective red, green, and blue light.
On the other hand, it is important to develop technology of organic EL light-emitting element which allows the use of a large size substrate, aiming at manufacturing large-size organic EL light-emitting elements and at reducing costs.
Recently, much attention has been paid to the following two methods of forming organic EL light-emitting elements through the use of a large size substrate.
One is such that white-color organic EL elements are formed over the entire region of display, and color display is performed by using a four-color filter for red, green, blue, and white colors. This method is effective in forming a large screen, a high definition display, and the like.
The other, an attention-getting method of forming organic EL light-emitting elements on a large size substrate, is such that organic EL light-emitting parts are formed by a coating method. As the coating method, various processes have been examined which can be divided broadly into two categories: That is, one includes relief printing, flexographic printing, screen printing, and gravure printing, and the other includes inkjet printing (see, Japanese Patent Unexamined Publication No. 2011-249089).